Mushroomed case

[versifier]

some of this stuff versifier and I am able to answer just because....well.... we bent, broke, mangeled. stuck,oopsied and other words.... equipment, brass, bullets, dies, stocks, blueing. recoil pads.

Truth is where you find it.

[atr]

R5R and Versifier have the problem nailed for you.....its all in the crimping.

Just be aware that with a roll crimp (which is what I use) the case length is critical. Any variation in case length will cause more or less pressure during the crimping process. I would bet that your cases with the distortion were longer in length than those without the distortion. You might check your case lengths. You might also want to invest in a taper crimp die.